if one wing is going to stall before the other,...I would think you'd want the bottom wing to stall first. it carries more weight per foot because it is usually smaller and when stalled, you still have the secure geometry of a parasol wing arrangement with the top wing still flying. I guess i look at the importance of the plane being more snap-roll friendly with the top wing not flying as insignificant in the scope of overall handling. I would much rather have good landing approach manners than snap-roll readiness.
I wonder if Mr. Whitehead has the right idea,,,, both wings should be contributing their proportion to flight equally and the bottom wing will quit all by itself when the time is right, simply because it is usually smaller and more heavily loaded.
wash out or not, probably depends on how you look at the "which wing stalls first" aspect. if the bottom wing gives up first, then I'd want some wash-out in the top wing. I can't see an instance where I would want the top wing to stall first,....to me,.... that just doesn't make any sense in the scope of stability.